A private U.S. airborne surveillance company has confirmed one of its planes is missing in Angola.

A spokesman for the Florida-based firm Airscan says one of its twin-engine Cessna 337s has been missing in Angola since July 16. There were two crewmen on board, both U.S.-trained Angolan contract employees of the firm, which provides airborne security for oil installations in the African country.

The spokesman says the plane went missing while on a nighttime surveillance mission out of the northwestern town of Soyo. He says it is not known whether the aircraft may have been fired on by rebels of Angola's UNITA movement or whether it suffered a mechanical problem.

The spokesman says a search is continuing for the missing plane and its crew. A second Airscan surveillance aircraft based in Angola is helping in the search operation.

The spokesman says Airscan is very concerned and is keeping in close touch with the families of the two missing crewmen - the plane's pilot and its surveillance systems operator.

Airscan has been operating in Angola since 1993 - providing security for the oil industry. In addition to airborne surveillance, the spokesman says, the firm established ground security for a major oil installation in the enclave of Cabinda as well as offshore sea patrols. He says both operations are now fully run by Angolans trained by Airscan.

The airborne operation is carried out by both Angolans and Americans. The spokesman says Airscan teams have flown over 15,000 hours of missions in Angola.

He says this is the first time any of its planes has ever been lost in Angola or elsewhere.

Airscan conducts missions for various clients in the United States, South America and Africa. It has recently conducted surveillance operations for the U.S. military in the Balkans.

The spokesman says surveillance equipment on board the firm's planes in Angola has been used to detect any threatening movements near oil facilities. Angola's UNITA rebels have attacked oil installations in the past.

The spokesman denies the firm has ever been approached by Angolan authorities to help in the search for fugitive UNITA rebel leader Jonas Savimbi. He also says it has never been asked to assist security forces in Cabinda in the search for kidnap victims held by guerrilla groups operating in the northern enclave.